On 10 October 1915, while flying two-seaters in FFA 3b as an artillery spotting observer, Greim claimed his first aerial victory: a Farman. He also served with FAA 204 over the Somme. After undergoing pilot training, Greim joined FA 46b on 22 February 1917.[1]

Greim transferred to Jagdstaffel 34 in April 1917. He scored a kill on 25 May 1917, the same day he received the Iron Cross First Class. On 19 June, he rose to command Jasta 34. Greim became an ace on 16 August 1917, when he shot down a Sopwith 1 1/2 Strutter. By 16 October, his victory tally totaled 7. There was a lull in his successes until February 1918. On the 11th, he had an unconfirmed victory and on the 18th he notched up aerial victory number 8.[1]

On 21 March 1918, the day of his ninth credited victory, Greim became Commanding Officer of Jagdgruppe 10. He flew with them until at least 18 June, when he notched up his 15th success. On 27 June 1918, while Greim was engaging a Bristol Fighter, his aircraft lost its cowling. The departing cowling damaged his top wing, along with the lower left interplane strut, but Greim managed to land the machine successfully.[1]

By 7 August 1918 he was commanding Jagdgruppe 9, and scored his 16th victory. On 23 August, he cooperated with Vizefeldwebel Johan Putz in what was arguably the first successful assault by aircraft on armored tanks.[2][3] On 27 September, he scored kill number 25 while flying with Jagdgruppe 9.[1]

He returned to Jasta 34 in October 1918. The Jasta had been re-equipped with 'cast-offs' from Richthofen's Flying Circus, Jagdgeschwader 1. The new equipment was warmly welcomed as being superior to the older Albatros and Pfalz fighters that they had been previously equipped with. Greim's final three victories came during this time, while he was flying Albatros D.Vs, Fokker Triplanes, and Fokker D.VIIs.[1]

By the war's end he had scored 28 victories and had been awarded the Pour le Mérite on 8 October, as well as the Bavarian Military Order of Max Joseph (Militär-Max Joseph-Orden).[1] This latter award made him a Knight (Ritter), and allowed him to add both this honorific title and the style 'von' to his name. Thus Robert Greim became Robert Ritter von Greim.[4]

After the war, Ritter von Greim returned to Bavaria and rejoined his regiment (8th Bavarian Artillery) and for 10 months ran the air postal station in Munich. This was the key turning point in his career, as in 1920 he flew the up-and-coming German army propaganda instructor Adolf Hitler to Berlin as an observer of the failed Kapp Putsch. Many other people from Hitler's years in Bavaria immediately after WW1 also rose to prominence in the National Socialist era. Greim then focused on a new career in law and succeeded in passing Germany's rigorous law exams. However, Chiang Kai-Shek's government offered him a job in Canton, China, to help to build a Chinese air force. Greim accepted the offer and took his family with him to China, where he founded a flying school and initiated measures for the development of an air force. His opinion of his Chinese pupils was not high, perhaps because of the belief among Europeans at the time that Asians were unable to operate complicated machinery. He wrote in a letter that "The Chinese will never make good fliers, they have absolutely no fine touch with the stick". Even before the Nazis came to power, Greim realized that his proper place was not in the expatriate community in China, but back home in Germany, and he returned to his native country.

Greim joined the Nazi Party and took part in the 1923 putsch; as a convinced Nazi he "remained utterly committed to Hitler to the very end of the war".[5]

In 1933, Hermann Göring invited Greim to help him to rebuild the German Air Force, and in 1934 was appointed to command the first fighter pilot school, following the closure of the secret flying school established near the city of Lipetsk in the Soviet Union during the closing days of the Weimar Republic. (Germany had been forbidden to have an air force under the terms of the Treaty of Versailles of 1919, so it had to train its pilots in secret.)

In 1938, Greim assumed command of the Luftwaffe research department. Later, he was given command of Jagdgeschwader 132 Richthofen (later JG 2), based in Döberitz, a fighter group named after Manfred von Richthofen.

Greim's greatest tactical achievement was his Luftflotte's involvement in the battle of Kursk and his planes' bombing of the Orelbulge. It was for this battle that Adolf Hitler awarded him the Knight's Cross of the Iron Cross with Oak Leaves (Das Ritterkreuz mit Eichenlaub des Eisernen Kreuzes), which made him one of the most highly decorated German military officers.

On 26 April 1945, when Soviet forces had encircled Berlin and the Third Reich was all but doomed, Generaloberst (Colonel-General) Ritter von Greim flew into Berlin from Rechlin with the notable female pilot Hanna Reitsch, in response to an order from Hitler. Initially they flew from the central Luftwaffe test facility airfield, the Erprobungsstelle Rechlin to Gatow (a district of south-western Berlin) in a Focke Wulf 190. As the cockpit only had room for the pilot, Reitsch flew in the tail of the plane, getting into it by climbing through a small emergency opening.[6] Having landed in Gatow, they changed planes to fly to the Chancellery; however, their Fieseler Storch was hit by anti-aircraft fire over the Grunewald. Greim was wounded in the right foot, and Hanna Reitsch took over the aircraft and landed on an improvised air strip in the Tiergarten, near the Brandenburg Gate.[7]

Hitler promoted Greim from General to Generalfeldmarschall (Field Marshal), making him the last German officer ever to achieve that rank, and then finally appointed him as commander in chief of the Luftwaffe, to replace Hermann Göring, whom he had had recently dismissed in absentia for treason. Greim thus became the second man to command the German Air Force during the Third Reich. However, with the end of the war in Europe fast approaching, his tenure as Oberbefehlshaber der Luftwaffe lasted only a few days.

On 28 April, Hitler ordered Ritter von Greim to leave Berlin and had Reitsch fly him to Plön, so that he could arrest Heinrich Himmler on the charge of treason. That night, the two only just managed to get away from Berlin, taking off from the Tiergarten air strip in a small Arado Ar 96 aircraft, before the eyes of soldiers of the Soviet 3rd Shock Army, who initially feared they had just seen Hitler himself escape. Later, in an interview, both Greim and Reitsch kept repeating: "It was the blackest day when we could not die at our Führer's side." Then they added, as tears kept running down Reitsch's cheeks, "We should all kneel down in reverence and prayer before the altar of the Fatherland." When asked what the "Altar of the Fatherland" was, completely taken aback, they responded: "Why, the Fuhrer's bunker in Berlin...."[8]

On 8 May, the same day as the surrender of the Third Reich, Ritter von Greim was captured by American soldiers in Austria. His initial statement to his captors was " I am the head of the Luftwaffe, but I have no Luftwaffe".[9] Ritter von Greim was scheduled to be part of a Soviet-American prisoner exchange program but fearing torture and execution at the hands of Joseph Stalin's secret police, the NKVD, he committed suicide with a cyanide capsule in Salzburg, Austria, on 24 May.[10]

^Hans Dollinger, The Decline and Fall of Nazi Germany and Imperial Japan: A Pictorial History of the Final Days of World War II, tr. Arnold Pomerans, Feltham: Hamlyn Odhams / New York: Crown, 1968, OCLC721310250, p. 228.